City of Light: The Story of Fiber Optics

The Importance of Being Digital
A DEMONSTRATION FOR THE QUEEN 163
The spread of digital pulse-code modulation in the telephone industry brought
honors to Alec Reeves from his fellow engineers, recognizing the technology
he invented a generation earlier. 16 Invited to give the 1969 John Logie Baird
Memorial Lecture at the University of Strathclyde, the aging visionary talked
of future fiber-optic communication. 16 In the fall of 1969, he told South African
engineers that within a half century, ‘‘The main overland and submarine
information highways will consist of wide-band optical quadratic-law
[graded-index] fibers with laser-type repeaters spaced just over two kilometers
apart.’’ 17
ITT gave Reeves an award and a $5000 honorarium when he retired at
68 at the end of 1970. Intending to remain active in engineering as well as
dabble in the paranormal, he formed Reeves Telecommunication Laboratories
Ltd. in London with Charles Eaglesfield and another engineer. They landed a
Post Office research contract, but years of heavy smoking caught up with
Reeves. He fell ill with lung cancer and died October 13, 1971, in London,
having done his part to launch the new technology. 18
By then, F. F. Roberts had become the central figure in British fiber-optic
research. Dedicated, energetic, and efficient, the crusty career technocrat focused
British fiber-optic development on meeting the practical needs of the
Post Office’s telephone division. He concentrated on testing the technology,
looking for potential fatal flaws as well as pushing the state of the art. 19 Top
management had already committed to digital transmission, made practical
by the advent of transistors and the integrated circuit, 20 so he concentrated
on digital systems.
Other system trials also yielded encouraging results. The University of
Southampton sent live BBC color-television signals through 1.25 kilometers
of experimental fiber and later repeated the experiments with French and
German television. 21 By late 1972, Chown could switch a narrow-stripe
double-heterojunction on and off up to a billion times per second. That meant
the laser could transmit a billion bits per second. 22
The experiments showed fiber-optic systems handled digital signals well.
In fact, semiconductor lasers worked much better for digital signal than for
analog ones. The light output of early semiconductor lasers did not increase
evenly with their drive current, so they could distort analog signals, like a
bad audio amplifier or speaker jumbles sound. Digital signals are immune to
such distortion, because systems need not detect the precise signal level, but
only if the signal is on or off. That doesn’t require high-fidelity reproduction—
a doorbell buzzer, a damaged speaker, or a semiconductor laser will suffice.
A Well-Planned Future Begins to Go Awry
On the other side of the Atlantic, AT&T had begun going digital in 1962.
The first step was the ‘‘T1 carrier,’’ running between urban switching centers.